After leaving the heart, blood returns to the heart via arteries, capillaries, and veins in a unidirectional blood flow cycle in which venous valves play an important role. Particularly in the lower extremities, the return of blood needs to resist the gravitational force generated by the blood column, and the coordinated opening and closing of the valves allows the blood column to be truncated step by step to ensure that the negative pressure in the chest cavity is sufficient to attract the return of blood flow to the heart. Once the valves of the deep veins of the lower extremities become diseased, a series of clinical conditions are triggered by the reversal of blood flow, which is known as deep venous insufficiency of the lower extremities. Valves can occur anywhere along the length of the vein, but are mainly located distal to the branch veins before entering the main trunk. If the location of the valve is not related to the site of venous bifurcation, it is called a free valve. The valves are most commonly bivalvular in shape, and may occasionally be found as single, triple, or as quadruple valves. The circular sinus, separated by two leaflets, is the basic structure of the valve and contains the leaflets, the free edge, the attachment edge, and the junction. The organization of the valve is very fine. Under light microscopy, the wall of the sinus and the leaflets are covered with only one layer of endothelial cells, which is followed by a thin elastic, fibrous, and collagenous connective tissue. Electron microscopy revealed a high number of smooth muscle cells at the leaflet junctions, suggesting a possible association with valve opening and closing. Although the valve tissue structure is very fine, its mechanical properties are excellent. Ackroyad et al. found that the tensile strength of the leaflet tissue was 9 N/mm2, whereas the relative tensile strength of the tissue around the sinus and the venous wall was only 5 N/mm2 and 2.5 N/mm2, respectively.With the exception of the plantar sinus, the lower the position of the limb, the higher the frequency of venous valves. In the deep venous system of the lower extremities, there are two locations where the valves are in a more constant position. In 90% of limbs, valves are present distal to the junction of the superficial and deep femoral veins, whereas in 96% of limbs, valves are present where the N vein enters the innominate muscular canal. Unlike cardiac valves, venous valves do not have a regular cycle of activity. When the body is in a standing or sitting position, venous blood flow is relatively constant, the valves are open, and the venous pressure is an iteration of column pressure, hydrostatic pressure, and central venous pressure. When the calf muscle pump contracts, the intermuscular venous blood is squeezed out and the venous pressure falls to zero, at which point the valve’s role is to maintain the lowered venous pressure and prevent backflow of blood. The coordination of valves with the rhythmic movements of the muscles becomes even more important when walking. In addition, valves have a role in keeping blood pressure stable within the venous system. When changing position or coughing violently, the venous valves close immediately to reduce the propagation of the sudden increase in pressure to the distal veins. At the end of an exercise cycle, when the muscle pump stops contracting, the valves remain closed for some time to avoid a sudden shock to the limb from accumulated hydrostatic pressure. The slowly increasing venous pressure reflects the shielding effect of the valve against hydrostatic pressure and also allows the slow return of blood from the capillary bed into the venous system. The valves’ hysteresis of changes in venous pressure also prevents sudden volume changes to minimize the pooling of blood in the lower extremities during rapid standing. Venous valve activity is closely related to the calf muscle pump exercise cycle, but not all valve activity is the same during the same muscle pump exercise cycle. When the calf muscle pump contracts, both the transportation venous valves and the venous valves downstream of the muscle pump close, and the pattern of activity of these valves is similar to that of the mitral valve. Axial veins, such as the N vein and the femoral vein, have sequential valves that open during muscle pump contraction, and the activity of these valves is similar to that of the aortic valve. When the calf muscle pump is diastolic, the activity of the valves is the opposite of that during contraction.